<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title></title>
</head>
<body>
<script type="text/javascript">
	var str ='123',num=100,bol = true

	//初始化
	//重新声明 JavaScript 变量，该变量的值不会丢失
	var str,num ,bol

	str = undefined
	num = undefined
	bol = undefined

	console.log(str)
	console.log(num)
	console.log(bol)

</script>
</body>
</html>